This invention relates to an apparatus which utilize utilizes an optical fiber loop based RF signal train generator to store transient pulses and regenerate their identical replicas for analysis. The present invention drastically increases our abilities to investigate acoustical, electromagnetic, and optical transient phenomena.
Interferometer is a widely used instrument. The constituents of interferometers may vary, but they all comprise these essential elements: a source, a splitter, two paths, and a detection apparatus. The source may generate acoustical, electromagnetic, and light wave, which is split into two paths by the splitter. The detection apparatus compares waves from the two paths, and determine determines their variational differences. Interferometer is a powerful instrument, which is capable of probing micro, meso, and macro systems. A system under test may be the source, the splitter, or an external system inserted into an interferometer path. We can infer the physical characteristics of the system under test from the observed variational differences.
An interferometer with a continuous wave source requires both the interferometer and system under test to be stable and stationary. Any random and vibrational motion will blur the variational differences, and mask the physical characteristics of the system under test. An interferometer with a short-pulsed source will freeze a transient natural event. However, with a conventional interferometer we are not able to decipher completely the variational difference created by a single transient event. Multiple pulses and events are needed, thus the short pulse and the transient event have to be exactly and repeatedly reproduced. This may not be possible with all transient events.
Digitizing receiver is another widely used instrument. It comprises a radio frequency (RF) receiver and a digitizer. In a receiving process, the RF receiver first converts an RF signal to an intermediate frequency (IF) signal, and then to a video signal. A digitizer converts the analog video signal to a digital signal. The capability of a digitizer depends on its sampling rate. Digitizers with sampling rate of 200 MHz are commercially available. Digitizers with sampling rate of 1 GHz have been reported. Depending on the capability of a digitizer, the down conversion to a video signal may not be needed and a digitizer may directly digitize a an IF signal. A down conversion will filter away many intrinsic traits of a transient event. Most radar receivers have IF frequency of 60 MHz. More sophisticated RF receivers have IF frequency of 10 GHz to preserve the intrinsic traits of subnanosecond RF pulses. It is still impossible for a digitizing receiver to completely capture the intrinsic traits of a single RF pulse with frequency of 10 GHz and pulse width of 1 GHz. Multiple pulses and events are again needed.
In light of the above, there is a need in the art for a new apparatus which are is capable of capturing the intrinsic traits of and determining the variational differences created by a random, chaotic, turbulent, or transient phenomenon. Furthermore it will reveal the physical traits of a single transient event without instability blurring. An interferoceiver with RF signal train generator will fulfill the needs to capture transient traits and to overcome the blurring. The physical principle for the new interferoceiver to capture an a transient event is the same as that for optical fiber based radars with an RF signal train generator.
The conventional method, which rests on the available technology. As the technology evolves, we are able to decipher a single transient event completely. The technology is the optical fiber RF delay loop based RF signal train generator. The information concerns the delay loop and generator can be found in the parent patent applications. With their help, a radar is able to determine the range and Doppler shift of a target with a single radar pulse. We will give a brief discussion here on the RF signal train generation.
Let us assume the single input RF pulse to the loop has the form
A(txe2x88x92ti) Exp{+j xcfx89t}, xe2x80x83xe2x80x83(1) 
where xcfx89 is the circular frequency of the RF pulse with a pulse profile A (t-ti) centered at the time ti. Experimentally we can not decipher the intrinsic characteristics of a short RF pulse. It is the limitation imposed by the sampling rate and Nyquist theorem. RF pulses are transient. Media were not available to record a transient RF: pulse faithfully for the examination at a later time. Since the experimental means did not exist for completely deciphering a short RF pulse, we had to rely on the alternative alternate methods. These methods are only useful to those short RF pulses which can be reproduced exactly by their respective sources. We then examine a portion of each reproduced pulse. The information from the reproduced pulses are is aggregated to complete the deciphering of a short RF pulse. A sample oscilloscope uses such a method to decipher a short RF pulse.
Now the optical fiber RF delay loop provides an alternative alternate method. The delay loop causes the pulse delay of the input RF pulse. The pulse train emerged from the optical fiber delay loop can be expressed as                                           ∑                          i              =              1                        N                    ⁢                                    A              ⁡                              (                                  t                  -                                      t                    i                                                  )                                      ⁢            Exp            ⁢                          {                                                +                  j                                ⁢                                  xe2x80x83                                ⁢                ω                ⁢                                  xe2x80x83                                ⁢                t                            }                                      ,                            (        2        )            
where N is the number of pulses in the train, xcfx84 the time delay of the loop, and ti=ixc3x97xcfx84 denotes the time delay of a an RF pulse emerged from the storage loop after looping i times. The delay caused by an optical fiber is a dynamical delay. RF pulse in the emerging train replicates the input RF pulse. By examining the copies of its replicas, a short RF pulse can be completely deciphered and repeatedly examined. It is impossible with a conventional digitizing receiver or interferometer.
A reference pulse is required in deciphering an RF pulse. It plays two roles. These are the triggering in a digitizing receiver and the referencing in an interferometer. The triggering instructs the digitizer when to sample. The referencing provides an interferometer with a basis in evaluating what a transient phenomenon has affected the probing pulse. An additional optical fiber RF delay loop has to be introduced in yielding a reference pulse train. An RF signal train generator comprises two identical optical fiber RF delay loops, which will fulfill the needs. We then examine each copy of the RF pulse replicas with the help from a copy of the reference pulse replicas.
Pulsed signals may be acoustical, electromagnetic, and optical. These pulse signals in their respective receivers and interferometers will be eventually converted to the electromagnetic pulse signals. Hence, RF signal train generators can be coupled with acoustical, electromagnetic, and optical signals to investigate their respective phenomena.
Embodiments of the present invention, which has a board functional capability, advantageously satisfy the above identified needs in the art. Embodiments of the present invention will provide an interferoceiver which is versatile and sophisticated. Such an interferoceiver will capture the intrinsic characteristics of a transient event without the blurring from its instability. In particular, embodiments of the present invention comprise optical fiber RF delay loops for storing short pulses, and reproducing their identical replicas.
In preferred embodiments of the present invention, the interferoceivers are equipped with an RF signal train generator, digitizing and intra pulse coherent processing subsystems. As a result, a new interferoceiver will be able to freeze a transient event, and will have the functional capabilities of determining the statistical distribution, which describes the instability of random, chaotic, turbulent, and transient phenomena. As those of ordinary skill in the art will readily appreciate, in the light of intra pulse coherence, the instability blurring associated with multiple pulses will no longer be a problem, and external interferences from other sources will be drastically reduced.
In other embodiments of the present invention, the RF signal train generator, digitizing and intra pulse coherent processing subsystems are directly added to conventional digitizers and interferometers to upgrade their functional capabilities as well as removing multiple pulse requirements for these instruments.